All visitors have the same IP (only one website)

Hello,
Visitors on only one website have the same IP. For other websites does’t have this problem - correctly recognizes the visitor’s IP.

What is the cause?
Thanks,

Are you using CloudFlare or a similar service?

I’m not sure if the server doesn’t use a proxy. I checked in phpinfo:

SERVER_ADDR: XXX.XXX.100.130
while IP address of a website is: XXX.XX.104.160

What should I do?

I found this faq. Which code should I use?
proxy_host_headers is SERVER_ADDR?
;proxy_host_headers is IP address of a website?

[General]
; Uncomment line below if you use a standard proxy
;proxy_client_headers[] = HTTP_X_FORWARDED_FOR
;proxy_host_headers[] = HTTP_X_FORWARDED_HOST

; Uncomment line below if you use CloudFlare
;proxy_client_headers[] = HTTP_CF_CONNECTING_IP

; Uncomment line below if you use another proxy (that sets Client-IP header)
;proxy_client_headers[] = HTTP_CLIENT_IP